1. Field of the Invention
The present invention relates to telescoping crane booms; and more particularly, it relates to an improved arrangement of web stiffening members on the side webs of each of the variably movable boom sections of a crane boom assembly.
The boom sections of a telescoping crane boom may be of any cross sectional configuration but are typically rectangular in transverse cross section. Two or more box shaped boom sections are correspondingly proportioned so that they telescopically slide in each other to provide a boom of appropriate length. Generally, a telescoping crane boom has from two to five nested boom sections. Each boom section comprises a top plate, a pair of side webs extending downwardly from opposite longitudinal edges of the top plate and appropriately secured thereto as by welding and a bottom plate suitably welded to the side webs to close the boom section. In an effort to increase the load carrying capacity and improve the longitudinal stability of the crane boom, reinforcements have been provided in the side webs.
2. Known Systems
Web stiffeners have been deployed on the side walls of the boom section in varying design configurations so as to increase the load carrying capability of the crane boom and to improve its longitudinal rigidity.
For example, as shown in U.S. Pat. No. 3,445,004, issued May 20, 1969 to Grider et al, the web stiffener members are arranged on the side webs of the boom in a lattice configuration which can be described as a simulated Warren truss. Although the simulated Warren truss arrangement does improve the load bearing capability of the crane boom, such a web stiffener arrangement does not substantially improve shear stress capabilities. Further, the simulated Warren truss arrangement fails to provide for changes in load distribution along the length of the boom section and thus would fail to minimize tensile stress in the web and compressive stress in the web stiffeners at all instances of critical load changes along the length of each boom section.
A second form of truss arrangement for the web stiffeners is disclosed in U.S. Pat. No. 3,708,937 issued on Jan. 9, 1973 to Sterner. The Sterner patent discloses a web structure with the web stiffeners mounted on the side webs of the boom in a simulated Pratt truss configuration which comprises a series of vertically oriented web stiffening members arranged in longitudinally spaced relationship along each side web of the boom sections. In the above patent the web stiffening members are shown as appropriately secured to the side webs as by welding and similarly secured to respective top and bottom plates of the boom section in perpendicularly aligned longitudinal spaced relation. However, the simulated Pratt truss configuration also fails to provide adequate protection against shear forces and further does not provide a suitable arrangement to minimize tensile stress in the web and compressive stress in the web stiffeners so as to improve the longitudinal rigidity and the load bearing capability of the crane boom.